1. Field of the Invention
The invention relates to a buckle folding unit or pocket folding unit having an adjustable folding pocket. The invention also relates to a method for controlling the register of a buckle folding unit.
Heretofore known buckle folding units have three folding rollers which are jointly driven and rotate at the same speed, and a folding pocket. The folding rollers are essentially arranged at the corners of a right-angled triangle, the two folding rollers that are disposed vertically above one another conveying the incoming sheet into the folding pocket as far as a pocket stop that is adjustable as desired. The sheet is conveyed into the pocket at a travel speed that is matched to the composition of the paper. When the leading edge of the sheet strikes the pocket stop, and if the sheet is simultaneously conveyed further, a suspended buckle fold is formed in the buckling space between the three folding rollers, and the fold is gripped by the two folding rollers which are disposed horizontally beside one another and rotate in opposite directions. As the buckle fold passes through the folding rollers, the fold is then formed. The pocket stop, the width of the folding pocket and the position of the pocket mouth and of the pocket lips in relation to the buckling space have to be adjusted to the quality of the paper that is used and to the sheet format. These adjustments must also be made if the atmospheric humidity changes, because the stiffness of the paper is changed thereby. Furthermore, a change in the production speed has the effect of a change in the deformation of the sheet in the folding pocket and in the buckling space, so that the position of the fold on the sheet is displaced, and the folding unit may possibly have to be readjusted. The positional deviation of the fold on the sheet can, in this regard, only be detected on the finished folded sheet.
2. Summary of the Invention
It is an object of the invention to provide a buckle folding unit with which deviations of the fold position on a folded sheet can be detected during production. It is, furthermore, an object of the invention to provide a buckle folding unit with which control of the position of the fold on the sheet is made possible. It is also an object of the invention to provide a method for controlling the register of a buckle folding unit which ensures a constant position of the fold on the sheet in the event of a change in the production speed or paper stiffness.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a buckle folding unit with a folding pocket having an adjustable pocket stop, comprising a first detector for detecting a first instant as a sheet travels from an inlet to the buckle folding unit until it reaches the pocket stop, a second detector for detecting a second instant as the sheet travels from a formation of a fold as far as an outlet from the folding pocket, and a device for determining a length of the sheet conveyed between the first and the second instants.
In accordance with another feature of the invention, the first detector serves for detecting entry of the sheet into the buckle folding unit.
In accordance with a further feature of the invention, the first detector for detecting entry of the sheet into the buckle folding unit has at least one optical sensor.
In accordance with an added feature of the invention, the folding pocket has a pocket mouth with a lower lip, and the second detector serves for detecting a deflection of the pocket lower lip as the fold is formed.
In accordance with an additional feature of the invention, the second detector serving for detecting the deflection of the pocket lower lip is constructed as a displacement detector.
In accordance with yet another feature of the invention, the second detector serving for detecting the deflection of the pocket lower lip has at least one optical sensor.
In accordance with yet a further feature of the invention, the second detector serving for detecting the deflection of the pocket lower lip has a wire strain-gauge device on the pocket lower lip.
In accordance with yet an added feature of the invention, the second detector serving for detecting the deflection of the pocket lower lip has a piezo-electric sensor disposed on the pocket lower lip.
In accordance with yet an additional feature of the invention, the first detector serves for detecting entry of the sheet into the folding pocket, and the second detector serves for detecting exit of the sheet from the folding pocket.
In accordance with still another feature of the invention, the folding pocket has a pocket mouth, and the first and the second detectors, respectively, serving for detecting entry and exit of the sheet, are arranged at the pocket mouth.
In accordance with still a further feature of the invention, the first and the second detectors, respectively, serving for detecting entry and exit of the sheet have a common optical sensor.
In accordance with still an added feature of the invention, the device for determining the length of the sheet conveyed between the first and the second instants has a pulse generator assigned to a folding roller, and a counting device.
In accordance with still an additional feature of the invention, the first detector for detecting the first instant serves for detecting a leading edge of the sheet at a defined position on a sheet path, and the second detector for detecting the second instant serves for detecting a folded edge of the sheet that has been folded.
In accordance with another feature of the invention, the second detector for detecting the folded edge of the sheet that has been folded includes a light barrier having a transmitter for emitting electromagnetic radiation and an associated receiver for receiving the electromagnetic radiation.
In accordance with a further feature of the invention, a straight connecting line between the transmitter and the receiver is disposed at an angle to the axes of the folding rollers.
In accordance with an added feature of the invention, the second detector for detecting the folded edge of the sheet that has been folded includes a light barrier having a laser-light transmitting unit and a laser-light receiver.
In accordance with an additional feature of the invention, the folding pocket is adjustable and has at least one electrically activated actuating device, and the buckle folding unit includes a control unit for processing signals from the first detector for detecting the first instant, the second detector for detecting the second instant, and the device for determining the length of the sheet conveyed between the first and the second instants, the electrically activated actuating device of the folding pocket being drivable by the length-determining device.
In accordance with yet another feature of the invention, the buckle folding unit includes a folding pocket stop adjustable by the electrically activated actuating device.
In accordance with yet a further feature of the invention, the folding pocket has a width that is adjustable by the electrically activated actuating device.
In accordance with yet an added feature of the invention, the buckle folding unit includes at least one folding pocket adjustable by the electrically activated actuating device.
In accordance with yet an additional feature of the invention, the folding pocket has a folding pocket mouth displaceable by the electrically activated actuating device for varying a buckling space in the folding pocket.
In accordance with still another feature of the invention, the control unit has a microprocessor.
In accordance with still a further feature of the invention, the buckle folding unit includes at least one optical sensor for detecting a start of a printed image on an incoming sheet.
In accordance with still an added feature of the invention, the control unit serves also for processing a signal from the optical sensor for detecting the start of a printed image.
In accordance with another aspect of the invention, there is provided a method for controlling the register of a buckle folding unit, which comprises determining, in a learning phase, a desired value of a length of a sheet conveyed between a first and a second instant, and controlling to the desired value, during production operation, a determined actual value of the conveyed length of the sheet by driving an electric actuating device.
In accordance with another mode, the method of the invention includes, for controlling to a start of a printed image on a sheet, determining for each incoming sheet, a difference in length between entry of the sheet and the start of the printed image on the sheet.
In accordance with a further mode, the method of the invention includes controlling out fluctuations in the length difference so as to maintain a constant relationship between the start of a printed image and the position of the fold.
In accordance with an added mode, the method of the invention includes correcting the desired value with the length difference between the entry of the sheet and the start of the printed image.
In accordance with a concomitant aspect of the invention, there is provided a folding machine having at least one buckle folding unit constructed in accordance with at least one of the foregoing features.
Thus, the invention provides a buckle folding unit having a folding pocket with an adjustable pocket stop, wherein a device is provided for detecting a first instant as a sheet runs from an inlet to the buckle folding unit until it reaches the pocket stop, a device is provided for detecting a second instant as the sheet runs from the formation of the fold as far as the outlet from the folding pocket, and a device is provided for detecting the sheet length conveyed between the first and second instants.
The invention is based upon the finding that the deviation of the position of the fold on the sheet depends upon the sheet length conveyed between an instant located before the sheet is buckled in the folding pocket or in the buckling space, and an instant at which the fold is formed, but can also be detected at an instant at which the formation of the fold has already been carried out and the buckling of the sheet is no longer present. In specific terms, if the sheet has a lower stiffness than its intended stiffness in set-up operation, then the sheet will be excessively deformed in the folding pocket or in the buckling space, so that a greater sheet length than in set-up operation will be conveyed into the folding pocket or the buckling space. Consequently, the formation of the fold takes place only at a later instant, after a greater sheet length has been conveyed than in set-up operation. The deviation of the position of the fold on the sheet can therefore be carried out by determining the sheet length conveyed up to the formation of the fold, but also by determining the sheet length conveyed up to an instant at which the formation of the fold has already taken place and the buckling of the sheet is no longer present. During set-up operation, a desired value, which identifies the proper formation of a fold, can be determined for the conveyed sheet length. The deviation in the position of the fold can therefore be determined through a deviation of the conveyed sheet length from the desired value.
In an improvement in the invention, provision is made for the folding pocket to have a pocket mouth with a lower lip, and for the device for detecting the second instant to be constructed as a device for detecting the deflection of the pocket lower lip as the fold is formed. At the instant at which the fold is formed, the part of the sheet that extends into the folding pocket rests on the pocket lower lip and exerts pressure on the latter. As a result, the pocket lower lip is deflected at the instant the fold is formed. Detecting the deflection of the pocket lower lip therefore provides a simple and reliable possibility for detecting the instant at which the fold is formed. The deflection of the pocket lower lip can be carried out in this case via wire strain gauges, piezo-electric sensors or optical sensors.
A further developed measure provides for the device for detecting the first instant to be constructed as a device for detecting the entry of the sheet into the folding pocket, and the device for detecting the second instant to be constructed as a device for detecting the exit of the sheet from the folding pocket. As a result of these measures, the deviation of the fold position can be detected via a distance measurement, specifically the conveyed sheet length, and in particular, exact detection of the instant at which the fold is formed is unnecessary.
Provision is further made for the folding pocket to have a pocket mouth, and for the device for detecting the entry of the sheet and the exit of the sheet to be arranged on the pocket mouth. In this way, the buckling of the sheet in the folding pocket over the entire length thereof can be taken into account, as a result of which the magnitude of the deviation from the desired value is relatively high, and the deviation is therefore easy to detect.
A further developing measure provides for the device for detecting the entry of the sheet and the device for detecting the exit of the sheet to have a common optical sensor. Such a construction of the buckle folding unit according to the invention is particularly simple and can be implemented cost-effectively. A deviation in the fold position can therefore be detected using only one optical sensor and a device for determining the conveyed sheet lengths. In the case of such an arrangement, the fold on the sheet is displaced by half the deviation of the conveyed sheet length from the desired value.
Moreover, provision is made for the adjustable folding pocket to have at least one electrically activated actuating device, and for a control unit which processes the signals from the device for detecting a first instant, the device for detecting a second instant, and the device for determining the sheet length conveyed between the first and second instants, and which drives the electrically activated actuating device of the folding pocket. Going beyond the simple detection of a displacement of the fold position on the sheet, this provides the possibility of automatically controlling out any deviation of the position of the fold in the sheet. Because the actuating device of the folding pocket is driven, the length of the portion of the sheet pushed into the folding pocket during the formation of the buckle fold in the buckling space can be influenced. It is thereby possible to compensate for changed deformation of the sheet during the buckling operation, for example, as a result of a higher production speed or a change in the paper stiffness. The actuating devices provided can be actuating motors provided with a potentiometer or stepping motors. The actuating device can displace, for example, a folding pocket stop, the folding pocket width, at least one folding pocket lip or the folding pocket mouth. The control unit advantageously has a microprocessor.
According to an advantageous development of the invention, optical sensors are also provided for detecting the start of the printed image on an incoming sheet. This embodiment of the invention is particularly advantageous when, for example, a brochure or a prospectus is to be produced, in which the printed image is displaced or fluctuates in relation to the sheet start. In the case of such sheets, the fold must be placed exactly in relation to the printed image, because otherwise, in the event of fluctuations between the sheet start and the start of the printed image, the edge has to be trimmed off from time to time. The detection of the start of the printed image is possible in a simple way using an optical sensor which measures the transmission or reflection of the sheet.
It is advantageous for the control unit also to process the signal from the sensor for detecting the start of the printed image. In the event of deviations in the position of the printed image on a sheet, too, the exact position of the fold can be secured by including the signal from the printed-image sensor. Faulty end products are thereby avoided.
The invention also provides a method for controlling the register of a buckle folding unit, according to which, in a learning phase, a desired value of the sheet length conveyed between the first and second instants is determined and, during production operation, a determined actual value of the sheet length conveyed is controlled to the desired value by driving the electrical actuating device. By employing such a method, after the learning phase has been concluded, the production speed of a folding machine provided, for example, with a number of buckle folding units according to the invention can be changed without requiring any adjustments to be performed manually. Using such a method, it is also possible to compensate for a change in the paper stiffness, for example, due to a varying atmospheric humidity.
In the case of controlling to the start of the printed image, provision is likewise made for a length difference between the entry of the sheet and the start of the printed image to be determined for each incoming sheet. A fluctuating length difference between the entry of the sheet and the start of the printed image, which would result in a fold position displaced in relation to the printed image, is recognized by this measure and can therefore be controlled out. This is preferably carried out by the desired value being corrected with the length difference between the entry of the sheet and the start of the printed image. By such a procedure, the required desired value is corrected only when control is directed to the start of the printed image, so that the method steps of controlling to the entry of the sheet can be maintained, and only have to be supplemented by a further correction step.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a buckle folding unit and a method for controlling the register of a buckle folding unit, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.